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Auto Exposure Bracketing in Auto ISO

Lee_Jay
Contributor

I have a 7D Mark II, but I understand this is the same with other cameras.

 

When you set auto ISO in manual mode, and change exposure compensation, it changes ISO.  Good.

 

When you set auto ISO in manual mode, and use auto exposure bracketing, it changes shutter speed.  Not good.

 

I understand the thinking here, even if I think it's wrong, so instead of just "fixing it", I'd recommend a custom function for selecting which you want it to do.  In my case, I actually want manual mode to behave like manual mode rather than behaving like Av mode which is the current behavior with AEB in manual mode.  If I had wanted the behavior to be like Av mode, I would have set it in Av mode!

30 REPLIES 30

TCampbell
Elite
Elite

@Lee_Jay wrote:

I have a 7D Mark II, but I understand this is the same with other cameras.

 

When you set auto ISO in manual mode, and change exposure compensation, it changes ISO.  Good.

 

I think you may find this depends on the camera mode.  Generally the camera follows something called the "program line".  In auto & semi-auto exposure modes, it tries to find a "safe" exposure (trying to find a reasonably safe shutter speed based on focal length of the lens and trying to find a safe f-stop given the aperture range of the lens.)  If the camera cannot open the aperture further AND slowing the shutter speed (relative to the focal length) would be unwise... then the safest thing to do is change the ISO.  

 

But the computer has "options" and, in my experience, which option it chooses depends on how much wiggle room it has with each element of the exposure (ISO, aperture, and shutter speed.)  You can read articles about how the "program line" works and realize the logic (what the camera will change is predictable -- and is based on which elements of the "exposure triangle" are already constrained.)

 

When you set auto ISO in manual mode, and use auto exposure bracketing, it changes shutter speed.  Not good.

 

The general recommendation in the industry when bracketing is that you should alter the shutter speed -- which is why the camera alters the shutter speed.

 

When you "bracket", the assumption is that you intend to use the bracketed data to merge for purposes of an HDR type result.  If you alter the aperture, then you change the depth of field.  This would be bad because you want all the samples to have identical depth of field with the ONLY variable being the amount of light collected.  If you change the ISO then you change the amount of noise and this may also be undesirable because you get a brighter exposure to integrate into the HDR result... but the "brighter" photo is now also noisier and that degrades the quality of the result.  

 

BUT... if you only change the shutter speed... you're generally safe.  The depth of field and noise levels should be consistent across all exposure samples in you bracketed series.  This means you may need a tripod.  That's probably ok, because bracketing doesn't work well for "action" photography (each image captures something completely different and you want a series of shots that captured the same thing... with only the exposure being different.)  This means you PROBABLY should be using a tripod anyway (otherwise you have to "register" (align) the frames because you didn't use a tripod... then crop.)

 

So... if you're using a tripod (and you should be) then the safest and best option to vary for a bracket image is... the shutter speed.  And that's exactly what the camera does.

 

I understand the thinking here, even if I think it's wrong, so instead of just "fixing it", I'd recommend a custom function for selecting which you want it to do.  In my case, I actually want manual mode to behave like manual mode rather than behaving like Av mode which is the current behavior with AEB in manual mode.  If I had wanted the behavior to be like Av mode, I would have set it in Av mode!


There's nothing magical about bracketing.  Some cameras have a built-in HDR mode which combines the images for you.  Some have a built-in "bracketing" mode which simplifies the task of gather a series of images where each has a slightly different exposure value (but doesn't combine them).  But it turns out photographers have been bracketing for years before any camera had any built-in feature for "bracketing".

 

Take a shot, alter your ISO, take another, alter the ISO again, and take another (then reset back to the original ISO).  The camera cannot stop you from doing that.   If you use the automatic bracketing feaure, it's going to use the shutter speed as the variable because that's the control that most photographers want to use -- and it's the method that would be taught in photography books and photography schools.

 

Tim Campbell
5D III, 5D IV, 60Da

The reason for needing ISO Bracketing is quiet simple. Flash.. Since Shutter speed effects only abient light, if someone is trying to create a HDR portrait, the only real option is ISO since aperture is not recommend at all for any bracketing.  So yes there needs to be an option to allow one to switch from Shutter Speed to ISO Speed..

I don't think having the noise level changing for an HDR shot is such a good idea.


@JoeJackson wrote:

The reason for needing ISO Bracketing is quiet simple. Flash.. Since Shutter speed effects only abient light, if someone is trying to create a HDR portrait, the only real option is ISO since aperture is not recommend at all for any bracketing.  So yes there needs to be an option to allow one to switch from Shutter Speed to ISO Speed..


Using Auto ISO during a series of AEB shots for HDR kind of defeats the whole purpose of taking a series of shots.  For HDR, you actually WANT to have under/over exposed shots.

 

For many of my HDR shots, my series of shots might look like this +1, 0, -1, -2, -3.  The shots are not centered around zero.  Adjusting the ISO over that wide of a range, 4 Ev,  would only introduce noise.

--------------------------------------------------------
"The right mouse button is your friend."

Yes I am fully aware of the downside of using ISO bracketing. I am a professional headshot and landscape photographer. However you still miss the point that this is the ONLY way to bracket for flash..  In addition this is an option on many other cameras.   Besides bracketing 100 200 400, or just 100 320 is not going to introduce any signifigant noise that anyone will notice.  This technique is used by many well known photographers like Joel Grimes to get HDR portraits, while still using studio strobes..


@JoeJackson wrote:

Yes I am fully aware of the downside of using ISO bracketing. I am a professional headshot and landscape photographer. However you still miss the point that this is the ONLY way to bracket for flash..  In addition this is an option on many other cameras.   Besides bracketing 100 200 400, or just 100 320 is not going to introduce any signifigant noise that anyone will notice.  This technique is used by many well known photographers like Joel Grimes to get HDR portraits, while still using studio strobes..


Forgive me if this is a stupid question, but if you're in a studio situation, where you presumably have full control over the lighting, why do you need to use HDR techniques at all? I had always assumed that those were nothing more than an imperfect workaround for situations where you can't control the light. What am I missing?

Bob
Philadelphia, Pennsylvania USA

B from B said, "... why do you need to use HDR techniques..."

 

HDR increase the dynamic range of the camera no matter where you shoot.  That is what the "D" stands for.

 

 A side form that, auto ISO is not only silly it is a dumb idea.Smiley Frustrated IMHO, of coures, as always.

EB
EOS 1DX and 1D Mk IV and less lenses then before!


@ebiggs1 wrote:

B from B said, "... why do you need to use HDR techniques..."

 

HDR increase the dynamic range of the camera no matter where you shoot.  That is what the "D" stands for.

 

 A side form that, auto ISO is not only silly it is a dumb idea.Smiley Frustrated IMHO, of coures, as always.


Cut it out, Ernie! Go back and read what I actually said. I wasn't questioning the use of HDR techniques; I was questioning their use when you already have control of the ambient light. As you've demonstrated on numerous occasions, HDR techniques can save a picture that would otherwise be ruined by blown highlights and/or harsh shadows. But in a studio situation, where those conditions should be preventable, what's the point?

Bob
Philadelphia, Pennsylvania USA

Robert, Robert, Robert,

"I was questioning their use when you already have control of the ambient light."

 

Whether you control the light or you don't does not guarrantee a reduction in DR.  Since you have never shot in a studio, how would you know?

DR is everywhere, my friend, not simply outdoors.

EB
EOS 1DX and 1D Mk IV and less lenses then before!
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